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175,000-year-old underground Neanderthal stone circle

Structure discovered in 1990s is ten times older than Lascaux cave paintings

Bruniquel Cave in southwest France was discovered by members of a local caving club in 1990. The cave’s entrance had been sealed by a landslide during the last Ice Age, but the cavers re-opened a narrow 30m (100 ft.) passage leading into a main gallery of chambers rich in stalagmites and stalactites. Some 336 m (1,000 ft.) from the entrance, they found strange complex of stone circles, constructed from broken stalagmites. Intrigued by the discovery, the cavers brought in archaeologist Francois Rouzaud to investigate.

The complex comprises two circles measuring 6.7 × 4.5 m (22 ft. x 14 ft. 9 in.) and 2.2 × 2.1 m (7 ft. 3 in. x 6 ft. 10 in.) and four smaller stacks of stalagmites, two of which are located inside the larger circle. Around 400 stalagmite fragments were used in the construction, half of which are mid-sections with the tip and base removed. The fragments were standardised in length, leaving no doubt that the structures had been constructed by humans. All six structures show extensive traces of fire, with many of the fragments showing signs of either blackening or reddening.

Rouzaud recovered a burned bone from the largest structure, which was radiocarbon dated and found to be 47,600 years old. This predates the arrival of modern humans in the region, but not sufficiently to rule out the possibility that they were the builders. The only other possibility was Neanderthals – which in the 1990s, was viewed as unlikely. The slow-to-die perception of Neanderthals as dimwits was even more prevalent then. Sadly, before further investigations could be carried, Francois Rouzaud died suddenly, aged just 50. With his death, all work at Bruniquel Cave ceased, and the enigmatic stone circles were forgotten until they came to the attention of geologist Sophie Verheyden.

Verheyden was curious as to why nobody had attempted to date the stalagmites. 47,600 years is close to the useful limit of radiocarbon dating, but uranium series dating can go back much further, and speleothem is very amenable to this method. By applying it to calcite layers that had formed over the stalagmite fragments after the complex was built, it would be fairly straightforward to determine when they had been broken off from the floor of the cave. Verheyden assembled a multi-disciplinary team including archaeologist Jacques Jaubert and geologist Dominique Genty and in 2013, after obtaining permission to study the cave, they resumed the investigation.

The results are reported in the online edition of the journal Nature and they suggest that the Bruniquel Cave stone circles are 176,500 years old – ten times older than the cave paintings of Lascaux. There is not the slightest possibility that they were the work of modern humans, who would not arrive for another 130 millennia. The only hominins living in southwestern France at that time were Neanderthals. The attribution of the Bruniquel constructions to Neanderthals demonstrates that they possessed the sophistication and organisational skills to heat and light a deep underground cavern while they built and used an elaborate structure of a type never before seen elsewhere.

The obvious question now is was the function of these structures, located at such a great distance from the cave entrance? There is no evidence that the cave was used as a living habitat. Had the stone circles dated to the Upper Palaeolithic, nobody would have doubted that the complex was a ritual centre of some kind. It is difficult to avoid the conclusion that it served this function for its Neanderthal builders and as such is further evidence of their capacity for symbolic behaviour.